One proposed hybrid vehicle has an engine, a planetary gear unit including a carrier and a ring gear respectively linked to a crankshaft of the engine and to a drive shaft, a first motor connected to a sun gear of the planetary gear unit, a second motor connected to the drive shaft, and a battery capable of transmitting electric power to and from the first motor and the second motor (see, for example, Japanese Patent Laid-Open Gazette No. 11-93727). In this proposed hybrid vehicle, the first motor is driven and controlled to regulate the rotation speed of the engine.